Abstract: In the presence of an interface (or bottom), the processing gain can be obtained in the ultrasonic selfadaptive focusing and the target detection of time reversal, but it can't distinguish the target from the interface due to the coherent superposition of the interface reflection wave and the target reflection wave. There exists same shortcoming in general pulse reflection method in ultrasonic flaw detection. A modified time reversal method (i.e. exchanging-element time reversal method) is proposed in this paper. With this method, the reflection waves on the interface from different element arrive on the receiver at different times and the coherent peak will disappear. Therefore, the target (flaw) can be distinguished from the interface.